http://avatar.wikia.com/wiki/KorraWell, I was kind of imagining something.
What if Aang's avatar awesomeness was so inspirational that numerous people from all nations came to seek his tutoring in the ways of the air nomads, and he maybe bestowed the first ones with Airbending...
I dunno, just a thought, but that would be freaking awesome.
I've always imagined that with Energybending, he could not only take away bending, but bestow it (or amplify or change current bending capabilities).
“…Judge not what a man has done, but judge what he could have done if he was a different bloke altogether. For art thou a leper? And a leper can changeth his spots…” --Rudy Wade, Misfits (Series 4, Episode 8)